KR20210022126A - Manufacturing method of hot-dip metal plating steel strip and continuous hot-dip metal plating equipment - Google Patents

Abstract

A method of manufacturing a hot-dip metal-plated steel strip capable of producing a high-quality hot-dip metal-plated steel strip sufficiently suppressing the occurrence of edge overcoat is provided. In the method for manufacturing a molten metal-plated steel strip disclosed in the present invention, gas is injected from a pair of gas wiping nozzles 20A and 20B to the steel strip S pulled up from the molten metal bath 14, When adjusting the adhesion amount of the molten metal on both sides, a pair of baffle plates 40, 42 are provided outside the both ends in the width direction of the steel strip, and the pair of baffle plates 40, 42 with respect to the bath surface of the molten metal bath It is characterized in that the height (B) of the lower end is set to be +50 mm or less with the upper side in the vertical direction as positive.

Description

Manufacturing method of hot-dip metal plating steel strip and continuous hot-dip metal plating equipment

The present invention relates to a method for producing a hot-dip metal-plated steel strip and a continuous hot-dip metal plating facility, and more particularly, to gas wiping for adjusting the adhesion amount of molten metal on the surface of the steel strip (hereinafter, also referred to as "plating adhesion amount").

In the continuous hot-dip metal plating line, as shown in FIG. 10, the steel strip S annealed in the continuous annealing furnace in a reducing atmosphere passes through the snout 10, and the molten metal in the plating bath 12 It is introduced continuously in bath 14. After that, the steel strip S is pulled up above the molten metal bath 14 through the sink roll 16 and the support roll 18 in the molten metal bath 14, and gas wiping nozzles 20A and 20B After being adjusted to a predetermined plating thickness by, it is cooled and guided to a post process. The gas wiping nozzles 20A and 20B are disposed above the plating bath 12 to face each other with the steel strip S interposed therebetween, and inject gas from the injection ports toward both sides of the steel strip S. By this gas wiping, excess molten metal is scraped off, the amount of plating deposited on the surface of the steel strip is adjusted, and the molten metal adhered to the surface of the steel strip is uniform in the plate width direction and the plate length direction. The gas wiping nozzles 20A and 20B are usually configured to have a width wider than the width of the steel strip in order to cope with various steel strip widths and to cope with positional displacement in the width direction when pulling up the steel strip. It extends outward from the end.

In such a gas wiping method, the gas ejected from a pair of gas wiping nozzles collides outside both ends in the width direction of the steel strip and the flow of gas is disturbed. The wiping force decreases in the region (edge portion) near both ends, and edge overcoat is likely to occur in which the amount of plating deposited on the edge portion of the steel strip surface is relatively large. In particular, when the adhesion amount is a high adhesion amount of 120 g/m 2 or more, an edge overcoat appears more remarkably. This is because the wiping force of the edge portion of the steel strip surface further decreases when operating at a low wiping gas pressure in order to obtain a high adhesion amount. Since the plated steel sheet in which such edge overcoat has occurred is cut before winding, it has a great influence on the yield of the plated steel sheet.

As a method of suppressing a plating surface defect called edge overcoat, the following method is known. In Patent Document 1, a pair of baffle plates are disposed on the outside of both ends in the width direction of the steel strip at the height at which the pair of gas wiping nozzles are installed, and sprayed from the pair of gas wiping nozzles by the baffle plate. A method of avoiding gas collisions is described. In Patent Document 1, it is described that edge overcoat can be suppressed by collision avoidance of this gas.

Japanese Unexamined Patent Publication No. 2012-21183

However, according to the investigation by the present inventors, in the method disclosed in Patent Document 1, although the edge overcoat was somewhat suppressed, it was found that the effect was insufficient.

Therefore, in view of the above problems, an object of the present invention is to provide a method for producing a hot-dip metal-plated steel strip and a continuous hot-dip metal plating facility capable of producing a high-quality hot-dip metal-plated steel strip that sufficiently suppresses the occurrence of edge overcoat.

In order to solve the above problems, the inventors of the present invention earnestly studied and obtained the following knowledge. That is, in Patent Document 1, a baffle plate is simply provided at a height at which the gas wiping nozzle is installed, and direct collision of gas from a pair of gas wiping nozzles disposed opposite to each other outside both ends in the width direction of the steel strip is prevented. It was a technical idea that it should be avoided. Therefore, as shown in FIG. 8, there was a relatively distance from the lower end of the baffle plate 60 to the bath surface. However, as a result of observing the edge portion of the surface of the steel plate at a position below the wiping nozzles 20A and 20B, a phenomenon in which molten metal stays and becomes a mass at the edge portion below the bottom of the baffle plate 60 was observed. Became. It is thought that edge overcoat is generated under the influence of this bulky molten metal.

This phenomenon is considered to be due to the following mechanism. That is, the gas colliding with both sides of the baffle plate 60 on the outer sides of both ends in the width direction of the steel strip S has a component in the direction perpendicular to the surface of the baffle plate 60 and the surface of the baffle plate 60 Descend along. Therefore, gas from both sides of the baffle plate 60 collides to some extent just below the lower end of the baffle plate, and turbulence occurs. Due to this turbulence, the wiping force decreases at the edge portion below the bottom of the baffle plate. That is, as shown in Fig. 8, in the wiping, in addition to the wiping action at the site (stationary point) where the gas collides with the steel strip S, the gas after the impact flows downward of the steel strip S to increase the shear force. The wiping action by exerting is also obtained. However, at the edge portion below the bottom of the baffle plate, due to the turbulence, the wiping action due to shearing force decreases. In the case where the edge portion having the reduced wiping force as described above extends in the vertical direction, the top dross (zinc oxide lump floating on the bath surface) raised by the steel strip cannot be sufficiently removed, or the molten metal pulled up cannot be removed from the edge portion. It stays while being oxidized and becomes a mass.

Therefore, the inventors of the present invention have obtained the idea that shortening the distance from the bottom of the baffle plate to the bath surface contributes to suppression of edge overcoat in order to shorten the length of the edge portion in the vertical direction as described above in which the wiping force has decreased. And, as a result of investigating the correlation between the distance from the lower end of the baffle plate to the bath surface and the occurrence of edge overcoat, it was found that the edge overcoat can be sufficiently suppressed by making the distance 50 mm or less.

The summary structure of the present invention completed based on the above findings is as follows.

[1] a steel strip is continuously immersed in a molten metal bath,

Gas is injected from a slit-shaped gas injection port extending wider than the steel strip along the width direction of the steel strip in a pair of gas wiping nozzles arranged across the steel strip to the steel strip pulled up from the molten metal bath. To adjust the adhesion amount of molten metal on both sides of the steel strip,

As a method of manufacturing a hot-dip metal-plated steel strip for continuously manufacturing a hot-dip metal-plated steel strip,

A pair of baffle plates are provided on the outside of both ends in the width direction of the steel strip so that a part of the front and back surfaces face the gas injection ports of the pair of gas wiping nozzles,

A method for producing a molten metal-plated steel strip, wherein the height (B) of the lower end of the pair of baffle plates with respect to the bath surface of the molten metal bath is set to +50 mm or less with the upper side in the vertical direction being positive.

[2] The method for producing a hot-dip metal-plated steel strip according to [1], wherein the height (B) is -10 mm or more.

[3] The pair of gas wiping nozzles are installed downward with respect to the horizontal plane so that the angle θ formed by the gas injection port with the horizontal plane is 10 degrees or more and 75 degrees or less. ].

[4] The component of the molten metal contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1% by mass, Ni: 0 to 0.1% by mass, and the remainder is composed of Zn and unavoidable impurities. ]-The method for producing the hot-dip metal-plated steel strip according to any one of [3].

[5] a plating bath containing molten metal and forming a molten metal bath,

It has a slit-shaped gas injection port which is arranged with a steel strip continuously pulled up from the molten metal bath and extends wider than the steel strip along the width direction of the steel strip, and injects gas from the gas injection port toward the steel strip. Thus, a pair of gas wiping nozzles for adjusting the amount of plating on both sides of the steel strip,

The steel strip has a pair of baffle plates arranged so as to face the gas injection ports of the pair of gas wiping nozzles on the outer sides of both ends in the width direction, and the molten metal bath with respect to the bath surface of the molten metal bath. A continuous hot-dip metal plating facility, wherein the height (B) of the lower end of the pair of baffle plates is +50 mm or less with the upper side in the vertical direction as a positive.

[6] The continuous hot-dip metal plating facility according to [5], wherein the height (B) is -10 mm or more.

[7] The pair of gas wiping nozzles are installed downward with respect to the horizontal plane so that the angle θ formed by the gas injection port with the horizontal plane is 10 degrees or more and 75 degrees or less. ], the continuous hot-dip metal plating equipment.

According to the method for producing a hot-dip metal-plated steel strip and a continuous hot-dip metal plating facility of the present invention, it is possible to manufacture a high-quality hot-dip metal-plated steel strip sufficiently suppressing the occurrence of edge overcoat.

1 is a schematic diagram showing a configuration of a continuous hot-dip metal plating facility 100 according to an embodiment of the present invention.
2 is a cross-sectional view perpendicular to the steel strip S of the gas wiping nozzle 20A in the embodiment of the present invention.
3 is a cross-sectional view perpendicular to the steel strip S of the gas wiping nozzle 20A in a state in which the nozzle angle θ is greater than 0 degrees in one embodiment of the present invention.
4 is an enlarged view of the baffle plate 40 of FIG. 1 and its periphery.
Fig. 5 is a top view of the gas wiping nozzles 20A and 20B of Fig. 1 and the periphery thereof.
6 is an enlarged view of an end portion of the steel strip in FIG. 5 in the width direction and its periphery.
7 is a perspective view of the baffle plate 40 of FIG. 1 and its periphery.
8 is a perspective view of a baffle plate 60 and its periphery in the prior art.
9 is a graph showing the relationship between the height (B) of the lower end of the baffle plate with respect to the bath surface and the edge overcoat rate (R).
10 is a schematic diagram showing the configuration of a general continuous hot-dip metal plating facility.

Referring to Fig. 1, a method of manufacturing a hot-dip metal-plated steel strip according to an embodiment of the present invention and a continuous hot-dip metal plating facility 100 (hereinafter, also simply referred to as a "plating facility") will be described.

Referring to FIG. 1, the plating facility 100 of the present embodiment includes a snout 10, a plating bath 12 for accommodating a molten metal, a sink roll 16, and a support roll 18. . The snout 10 is a member having a quadrangular cross section perpendicular to the traveling direction of the steel strip, which partitions the space through which the steel strip S passes, and the tip thereof is a molten metal bath 14 formed in the plating bath 12 Is immersed in. In one embodiment, the steel strip S annealed in a continuous annealing furnace in a reducing atmosphere passes through the snout 10 and is continuously introduced into the molten metal bath 14 in the plating bath 12. After that, the steel strip S is pulled up above the molten metal bath 14 through the sink roll 16 and the support roll 18 in the molten metal bath 14, and a pair of gas wiping nozzles 20A , 20B), after being adjusted to a predetermined plating thickness, it is cooled and guided to a post-process.

A pair of gas wiping nozzles 20A and 20B (hereinafter, also simply referred to as "nozzle") are disposed above the plating bath 12 to face each other with the steel strip S interposed therebetween. In addition to FIG. 1, referring to FIG. 2, the nozzle 20A sprays gas from the slit-shaped gas injection port 28 extending in the width direction of the steel strip from its tip toward the steel strip S to plate the surface of the steel strip. Adjust the amount of adhesion. The other nozzle 20B is also the same, and the excess molten metal is scraped off by these one pair of nozzles 20A, 20B, and the amount of plating on both sides of the steel strip S is adjusted, and further, the plate width direction and the plate It is equalized in the longitudinal direction.

As shown in Fig. 5, the nozzles 20A and 20B are usually configured to be longer than the width of the steel strip in order to cope with various steel strip widths, and to cope with a positional shift in the width direction when pulling up the steel strip. It extends outward from the end in the width direction. That is, the slit-shaped gas injection ports 28 of the nozzles 20A and 20B extend to a width wider than that of the steel strip along the width direction of the steel strip.

In addition, as shown in FIG. 2, the nozzle 20A has a nozzle header 22, and an upper nozzle member 24 and a lower nozzle member 26 connected to the nozzle header 22. The tip portions of the upper and lower nozzle members 24 and 26 have surfaces that face parallel to each other when viewed in a cross section perpendicular to the steel strip S, thereby forming a slit-shaped gas injection port 28. The gas injection port 28 extends in the plate width direction of the steel strip S. The longitudinal cross-sectional shape of the nozzle 20A is a tapered shape whose front is tapered toward the tip end. The thickness of the tip portions of the upper and lower nozzle members 24 and 26 may be about 1 to 3 mm. In addition, the opening width (nozzle gap) of the gas injection port is not particularly limited, but may be about 0.5 to 3.0 mm. Gas supplied from a gas supply mechanism (not shown) passes through the inside of the header 22 and passes through a gas flow path partitioned by the upper and lower nozzle members 24 and 26, and is injected from the gas injection port 28, It is sprayed on the surface of (S). The other nozzle 20B also has the same configuration. In the present invention, the pressure of the gas in the nozzle header 22 is defined as "header pressure (P)".

In the manufacturing method of the molten metal-plated steel strip of the present embodiment, the steel strip S is continuously immersed in the molten metal bath 14, and the steel strip S is pulled up from the molten metal bath 14. ), by injecting gas from a pair of gas wiping nozzles 20A and 20B disposed between them, adjusting the adhesion amount of molten metal on both sides of the steel strip S, and continuously producing a molten metal-plated steel strip. .

In addition to FIGS. 1 and 2, referring to FIGS. 4 to 6, in the present embodiment, on the outer side of both ends in the width direction of the steel strip S, preferably on the extension surface of the steel strip in the vicinity of the end portion in the width direction of the steel strip S. , A pair of baffle plates 40 and 42 are disposed. These baffle plates 40 and 42 are disposed between a pair of nozzles 20A and 20B. Accordingly, the front and back surfaces of the baffle plate face the gas injection ports 28 of the pair of nozzles 20A and 20B. The baffle plates 40 and 42 contribute to reduction of splash by avoiding direct collision between gases injected from the pair of nozzles 20A and 20B.

The shape of the baffle plates 40 and 42 is not particularly limited, but it is preferably a square as shown in FIG. 7, and two sides of which are preferably arranged parallel to the extension direction of the end portion in the width direction of the steel strip S. . The thickness of the baffle plates 40 and 42 is preferably 2 to 10 mm. When the plate thickness is 2 mm or more, the baffle plate is hardly deformed by the pressure of the wiping gas. If the plate thickness is 10 mm or less, the possibility of contact with the wiping nozzle or thermal deformation is low.

Here, in this embodiment, with reference to FIG. 4, the height B of the lower end of the pair of baffle plates 40 and 42 with respect to the bath surface of the molten metal bath 14 is +50 mm with the upper side in the vertical direction as positive. It is important to do the following. When the height (B) exceeds +50 mm, as shown in Fig. 8, the length in the vertical direction of the edge portion of the steel strip surface whose wiping force decreases due to turbulence occurring immediately below the baffle plate is also 50 mm. There will be excess. In that case, as described above, an edge overcoat occurs due to the molten metal remaining in the edge portion and forming a mass. In contrast, by setting the height B to +50 mm or less, the length of the edge portion of the steel strip surface in which the wiping force decreases in the vertical direction can also be shortened to 50 mm or less. As a result, edge overcoat is sufficiently suppressed. From the viewpoint of suppressing the edge overcoat more sufficiently, the height (B) is preferably +40 mm or less, more preferably +30 mm or less, and most preferably, the baffle plates 40 and 42 are made of molten metal. When immersed in a bath, that is, B = 0 mm or B <0 mm.

In particular, when the target plating thickness is 120 g/m2 or more and the header pressure (P) is 30 kPa or less and high adhesion/low gas pressure, the edge portion of the steel strip surface is top dross (zinc floating on the pot bath surface). The lump) becomes easy to roll up, and the edge overcoat tends to deteriorate. Therefore, the effect of suppressing edge overcoat according to the present invention is particularly remarkably obtained in the case of the above-described conditions. However, it is preferable that the header pressure P is 1 kPa or more.

Moreover, it is preferable to make height (B) -10 mm or more. Thereby, it is possible to reduce the possibility that the baffle plate contacts the support roll 18 in the molten metal bath, or the baffle plate hinders the flow of dross in the bath, resulting in an increase in dross defects.

In addition, in one example of operation, the height of the bath surface slightly changes during operation. Specifically, due to the removal of molten zinc by the steel strip, the height of the bath surface gradually decreases, but when the height of the bath surface decreases by about several mm, the ingot mass of the bath composition is gradually added during operation so that the original bath surface height is reached. do. The height of the bath can always be monitored by a laser displacement meter. Here, in the manufacturing method of the hot-dip metal-plated steel strip of this embodiment, since the effect of suppressing edge overcoat is obtained by wiping in a state where the height (B) is +50 mm or less, the height (B) is always +50 mm during operation. Although it is preferable to maintain the following state, it is not limited to this, and the case where it exceeds +50 mm temporarily during operation is also included. However, it is assumed that the continuous hot-dip metal plating facility of the present embodiment is controlled so that the height (B) is always maintained in a state of +50 mm or less during operation.

In addition, the height of the upper end of the baffle plates 40 and 42 is not particularly limited as long as it is higher than the position of the gas injection port 28, but from the viewpoint of reliably avoiding direct collision of gas, the gap center of the gas injection port 28 It is preferably 10 mm or more higher than the position, and from the viewpoint of not disposing the baffle plate to an unnecessary point, it is preferably 300 mm or less higher than the gap center position of the gas injection port 28.

Referring to FIG. 6, the distance E between the end portion in the width direction of the steel strip and the baffle plate is preferably 10 mm or less, and more preferably 5 mm or less. Thereby, it is possible to more reliably prevent direct collision of opposing classifications. Moreover, from the viewpoint of reducing the possibility of contacting the baffle plate when the steel strip is meandering, the distance E is preferably set to 3 mm or more.

The material of the baffle plate is not particularly limited. However, in this embodiment, since the baffle plate is close from the bath surface, a top dross or splash (splash of molten zinc) is adhered, and the possibility of alloying with the baffle plate and fixing is conceivable. In addition, when the baffle plate is immersed in the bath, it is necessary to consider not only the alloying but also thermal deformation. From this point of view, examples of the material of the baffle plate include those obtained by applying a boron nitride-based spray that is easy to repel zinc on an iron plate, and SUS316L, which is difficult to react with zinc. Further, ceramics such as alumina, silicon nitride, and silicon carbide are preferable because both alloying and thermal deformation can be suppressed.

With reference to FIG. 2, it is preferable that the nozzle height H is low. The lower the nozzle height H, the higher the temperature of the molten metal at the stagnation point and the lower the viscosity, the wiping can be performed at a low header pressure, and edge overcoat is less likely to occur. Moreover, since the length of the baffle plate can be shortened, the rigidity of the baffle plate can also be maintained. However, if the nozzle height is too low, a large amount of splash is generated at a high gas pressure, so it is necessary to adjust it to an appropriate height. From this point of view, the nozzle height H is preferably 50 mm or more, more preferably 80 mm or more, further preferably 450 mm or less, and more preferably 250 mm or less. .

Referring to FIG. 3, in the present embodiment, a pair of gas wiping nozzles 20A and 20B are in a horizontal plane so that the angle θ formed by the gas injection port 28 with the horizontal plane is 10 degrees or more and 75 degrees or less. It is preferable to be installed downwardly. Here, the "angle θ of the gas injection port with the horizontal plane" refers to a portion (parallel portion) in which the upper nozzle member 24 and the lower nozzle member 26 face each other to form a slit, as shown in FIG. 3. , As viewed from a cross-section perpendicular to the steel strip, the extension direction of the parallel portion refers to the angle formed by the horizontal plane. By setting the nozzle angle θ to 10 degrees or more, the shear force due to the wiping gas can be increased, the phenomenon of weakening the wiping force can be more easily prevented, and a remarkable edge overcoat suppressing effect can be obtained. On the other hand, when the nozzle angle θ exceeds 75 degrees, there is a risk that unstable pressure stagnation occurs and bath wrinkles are likely to occur. Therefore, the nozzle angle θ is preferably set to 75 degrees or less.

2 and 3, the distance (d) between the nozzle tip and the steel strip is not particularly limited, but from the viewpoint of reducing the possibility that the nozzle tip will contact the steel strip, it is set to 3 mm or more, and the viewpoint of saving the wiping gas. It is preferable to set it as 50 mm or less.

The gas injected from the gas wiping nozzle is not particularly limited, and may be, for example, air, but may be an inert gas. By setting it as an inert gas, since oxidation of the molten metal on the surface of a steel strip can be prevented, variation in the viscosity of the molten metal can be further suppressed. The inert gas may contain one or more of nitrogen, argon, helium, and carbon dioxide, but is not limited thereto.

In addition, in this embodiment, the component of the molten metal contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1% by mass, and Ni: 0 to 0.1% by mass, and the remainder is composed of Zn and unavoidable impurities. It is desirable. When Mg is contained in this manner, it has been confirmed that the molten metal is liable to be oxidized and the amount of top dross generation is increased, so that edge overcoat is liable to occur. Therefore, when the molten metal has the above component composition, the effect of suppressing the edge overcoat of the present invention is remarkably exhibited. Further, even when the composition of the molten metal is 5% by mass Al-Zn or 55% by mass Al-Zn, the effect of suppressing the edge overcoat of the present invention can be obtained.

The hot-dip galvanized steel strip produced by the production method and plating facility of the present invention includes a hot-dip galvanized steel sheet, which is a plated steel sheet (GI) that is not subjected to an alloying treatment after hot-dip galvanizing treatment, and an alloying treatment. All of the plated steel sheets (GA) to be applied are included.

Example

(Example 1)

In the hot-dip galvanized steel strip production line, a production test of the hot-dip galvanized steel strip was conducted. In each invention example and a comparative example, the plating equipment shown in FIG. 1 was used. As the gas wiping nozzle, one having a nozzle gap of 1.2 mm was used. In each Inventive Example and Comparative Example, the composition of the plating bath, the height of the bottom of the baffle plate with respect to the bath surface (B), the nozzle angle (θ), the wiping gas pressure (header pressure) (P), the distance between the nozzle tip and the steel strip (d) and the steel strip speed (L) were set to be shown in Table 1. The top of the baffle plate was set at a position 70 mm higher than the center of the gap of the gas injection port. The height H of the nozzle from the bath surface was set to 200 mm. Silicon nitride was used as the material of the baffle plate, the plate thickness was 3 mm, and the distance E between the end of the steel strip in the width direction and the baffle plate was 5 mm.

As a gas supply method to the gas wiping nozzle, a method of supplying a gas pressurized to a predetermined pressure by a compressor to the nozzle header was adopted. The gas species was air, and the temperature of the wiping gas was 100°C. In this way, a steel strip having a plate thickness of 1.2 mm x a plate width of 1000 mm was plated through a predetermined steel strip speed L to produce a hot-dip galvanized steel strip.

Moreover, the edge overcoat rate (R) of both sides of the produced hot-dip galvanized steel strip was calculated|required and evaluated in the following procedure. First, the target adhesion amount (CW) (g/m 2) of the total of both surfaces at each level is shown in Table 1. And, for the galvanized steel strips manufactured at each level, the actual adhesion amount (CWc) (g/m2) of the total amount of both sides of the steel sheet center portion and the actual adhesion amount (CWe) of the total amount of both surfaces of the steel sheet edge portion (g/m2) were measured. And the results are shown in Table 1. In addition, the measurement of CWc and CWe was carried out in conformity with JIS G3302 for one point on both sides, respectively. The edge overcoat rate (R) was calculated as (CWe/CWc-1) x 100 (%). Table 1 shows the results. In addition, in Table 1, in each plating type, the "edge overcoat improvement rate" with respect to the edge overcoat rate when there is no baffle plate is also shown. However, regarding plating type B, the improvement rates of Nos. 9 to 13 and 18 to 23 were based on No. 8, and the improvement rates of Nos. 15 to 17 were based on No. 14. The level at which the edge overcoat improvement rate was 50% or more was set as pass, and the level less than 50% was set as rejection.

As is clear from Table 1, when the height (B) of the bottom of the baffle plate to the bath surface satisfies 50 mm or less, the edge overcoat rate (R) is low, the edge overcoat improvement rate is 50% or more, and the plated steel sheet having good quality On the other hand, when the height (B) of the lower end of the baffle plate to the bath surface was out of the scope of the present invention, the edge overcoat rate (R) became large, and the edge overcoat improvement rate became less than 50%. In particular, for plating types B, E, and F, the effect when the height B of the lower end of the baffle plate with respect to the bath surface was in the range of the present invention was remarkably obtained.

(Example 2)

Using the plating equipment shown in Fig. 1, the height (B) of the lower end of the baffle plate with respect to the bath surface was changed in various ways, and a production test of a hot-dip galvanized steel strip was performed.

As the gas wiping nozzle, one having a nozzle gap of 1.2 mm was used. The composition of the plating bath was Al: 0.2% by mass and the balance was zinc. The nozzle angle (θ) was 0 degrees, the wiping gas pressure (header pressure) (P) was 8 kPa, the distance (d) between the nozzle tip and the steel strip was 10 mm, and the steel strip speed (L) was 50 m/min. . The upper end of the baffle plate was set at a position 70 mm higher than the center of the gap of the gas injection port. The height H of the nozzle from the bath surface was 200 mm. Silicon nitride was used as the material of the baffle plate, the plate thickness was 3 mm, and the distance E between the end of the steel strip in the width direction and the baffle plate was 5 mm.

In the same manner as in Example 1, the edge overcoat rate (R) was obtained, and the relationship between the height (B) of the lower end of the baffle plate to the bath surface was summarized in FIG. 9. Further, the edge portion of the steel strip surface was observed with a camera, and the state of the molten metal at the edge portion was confirmed.

As is clear from FIG. 9, the edge overcoat rate R was remarkably lowered by setting the nozzle lower end height B to 50 mm or less while being high when the nozzle lower end height B was 60 mm or more. In addition, when the height (B) of the lower end of the nozzle is 60 mm or more, molten metal that remains in the edge portion and becomes a mass is observed, whereas when the height of the lower end of the nozzle (B) is 50 mm or less, such mass No molten metal was observed, and the surface state of the molten metal was relatively uniform.

Industrial applicability

According to the method for producing a hot-dip metal-plated steel strip and a continuous hot-dip metal plating facility of the present invention, it is possible to manufacture a high-quality hot-dip metal-plated steel strip sufficiently suppressing the occurrence of edge overcoat.

100: continuous hot-dip metal plating equipment
10: Snout
12: plating bath
14: molten metal bath
16: sink roll
18: support roll
20A: gas wiping nozzle
20B: gas wiping nozzle
22: nozzle header
24: upper nozzle member
26: lower nozzle member
28: gas nozzle
40: baffle plate
42: baffle plate
S: Kangdae
B: Height of the bottom of the baffle plate to the bath surface
θ: The angle between the gas injection port and the horizontal plane
d: Distance between the tip of the nozzle and the pole
H: Nozzle height
E: Distance between the end of the steel strip in the width direction and the baffle plate

Claims (7)

The steel strip is continuously immersed in the molten metal bath
Gas is injected from a slit-shaped gas injection port that extends wider than the steel strip along the width direction of the steel strip in a pair of gas wiping nozzles arranged across the steel strip to the steel strip pulled up from the molten metal bath. To adjust the adhesion amount of molten metal on both sides of the steel strip,
As a method of manufacturing a hot-dip metal-plated steel strip for continuously manufacturing a hot-dip metal-plated steel strip,
A pair of baffle plates are provided on the outside of both ends in the width direction of the steel strip so that a part of the front and back surfaces face the gas injection ports of the pair of gas wiping nozzles,
A method for manufacturing a molten metal-plated steel strip, wherein the height (B) of the lower end of the pair of baffle plates with respect to the bath surface of the molten metal bath is set to be +50 mm or less with a positive upper side in the vertical direction. The method of claim 1,
The method for producing a hot-dip metal-plated steel strip, wherein the height (B) is -10 mm or more. The method according to claim 1 or 2,
The method of manufacturing a hot-dip metal-plated steel strip, wherein the pair of gas wiping nozzles are provided downward with respect to the horizontal plane so that an angle θ formed by the gas injection port with the horizontal plane is 10 degrees or more and 75 degrees or less. The method according to any one of claims 1 to 3,
The component of the molten metal contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1% by mass, and Ni: 0 to 0.1% by mass, and the balance consists of Zn and unavoidable impurities. Way. A plating bath containing molten metal and forming a molten metal bath,
It has a slit-shaped gas injection port which is arranged with a steel strip continuously pulled up from the molten metal bath between the steel strip and extends wider than the steel strip along the width direction of the steel strip, and the gas is injected from the gas injection port toward the steel strip Thus, a pair of gas wiping nozzles for adjusting the amount of plating on both sides of the steel strip,
A pair of baffle plates disposed on the outer sides of both ends in the width direction of the steel strip, and part of the front and back surfaces to face the gas injection ports of the pair of gas wiping nozzles
And a height (B) of the lower end of the pair of baffle plates with respect to the bath surface of the molten metal bath is +50 mm or less with a positive upper side in the vertical direction. The method of claim 5,
The continuous hot-dip metal plating facility, wherein the height (B) is -10 mm or more. The method according to claim 5 or 6,
The pair of gas wiping nozzles are installed downward with respect to the horizontal plane so that the angle θ formed by the gas injection port with the horizontal plane is 10 degrees or more and 75 degrees or less.

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